The present invention relates to a method of manufacturing a semiconductor device, particularly, a semiconductor device using a complex type (combination type) substrate prepared by detachably mounting a plurality of semiconductor substrates to a holder board during the manufacturing process.
In recent years, the semiconductor substrate for forming a semiconductor device is being made larger and larger in an attempt to facilitate mass production of the semiconductor device and to pursue the reduction in the manufacturing cost of the semiconductor device. However, in compliance with the demands for the large scale integration of the semiconductor circuit device, the manufacturing steps and apparatus are made highly complex, with the result that it is difficult to carry out uniformly the highly controlled manufacturing steps over the large area of the semiconductor substrate.
In, for example, a RIE (Reactive Ion Etching) step for anisotropically etching a surface of a semiconductor substrate in a vertical direction, it is necessary to form a uniform plasma over the entire surface of the substrate in order to process a substrate having a large diameter, e.g., a diameter of 8 inches, 12 inches or more. For forming a uniform plasma over the entire surface of a large substrate, various problems must be solved. For example, it is necessary to design appropriately a vacuum chamber of a large size, a vacuum pump of a large capacity for maintaining vacuum within the vacuum chamber, a mechanism for uniformly introducing an etching gas into the vacuum chamber, a device for a power supply for forming a uniform plasma, a means for uniformly introducing the plasma over the entire surface of the substrate, and a vacuum system for exhausting by products formed by the etching without impairing the uniformity of the plasma. It is also necessary to develop a heat exchanger system for maintaining constant the substrate temperature.
As pointed out above, it was necessary to develop a new RIE apparatus differing from the previous model every time the diameter of the semiconductor substrate was made larger.
Similarly, in order to deposit or form uniformly a film of a semiconductor material, an insulating material or a metallic material on a semiconductor substrate having a large diameter, it is absolutely necessary to improve the manufacturing apparatus to permit supplying film-forming materials uniformly over a large area of the substrate surface and to permit carrying out the reaction of the film-forming materials uniformly on the semiconductor substrate.
Also, in the heat treating steps for oxidation, diffusion of the electrically conductive impurities and their activation, it is necessary to maintain the temperature uniform over the large area of the semiconductor substrate. Further, it is necessary to take measures for maintaining the concentration and flow rate of the ambient gas uniform over the large area of the substrate surface. To meet these requirements, re-designing of the heat treating furnace, the heater or the lamp is required.
What should also be noted is that, even if the substrate can be heated uniformly, crystal defects such as slips and dislocations tend to be induced if stress is generated by the weight of the substrate itself, making it necessary to re-model the wafer holding equipment and the like.
As described above, in order to cope with the enlargement of the semiconductor substrate, it is necessary to develop and introduce a new manufacturing apparatus capable of coping with the enlargement of the semiconductor substrate in the individual manufacturing steps. It follows that, even if it is intended to achieve mass production of a semiconductor device by using a substrate having a large diameter in an attempt to reduce the manufacturing cost of the semiconductor device, the manufacturing process cannot be completed unless every single step included in the manufacturing process is ready for coping with the enlargement.
Particularly, it is impossible to achieve mass production of a semiconductor device using a substrate having a diameter larger than the semiconductor substrate on which the device is initially developed in the research and development stage, if it is impossible to cope with a large substrate in every manufacturing process. It impairs a smooth transfer of the researched and developed attainment to mass production, resulting in inefficient return on investment in research and development. What should be noted is that an intensive capital investment and the depreciation accompanying the investment offset the merit of the reduction of the manufacturing cost obtained by the improved productivity achieved by enlargement of the substrate.
In addition, it is technically difficult to manufacture a semiconductor substrate free from crystal defects over a large area of the substrate. When it comes to the CZ method, control of the heat flow within a melt and effect of the cooling after the crystal growth must also be taken into account. Heat tends to be confined within the crystal with increase in the diameter of the semiconductor substrate, leaving the substrate prone to oxygen precipitation. Also, it is necessary to polish flat the substrate surface over a large area. Such being the situation, it is unavoidable for the unit cost of the semiconductor substrate having a large diameter to be made higher and higher.
Further, in the conventional method of manufacturing a semiconductor device using a semiconductor substrate having a large diameter, where a process is not completed as intended in a part of a semiconductor substrate so as to give rise to defective regions or device malfunction, or where metal or other fine particles contaminate a part of the substrate it was unavoidable to discard the substrate with all the other functioning devices formed. Alternatively, it was unavoidable to continue the manufacturing process although the processes are to be performed in vain to some of the semiconductor devices which would fail to function. Particularly, where various functions are achieved on a single semiconductor substrate (System on Chip), or where an electronic circuit performing various functions is formed over the entire region of a semiconductor substrate (Wafer Scale Integration), the conventional manufacturing method is expected to be very low in yield.
For example, a one-chip system is known in which a memory function and a logic function for performing an arithmetic operation are formed on a single semiconductor substrate. In this case, the MOSFET performing the memory function is required to have a channel region having a high impurity concentration and a thick gate oxide film. On the other hand, the MOSFET included in the logic section is required to have a channel region having a low impurity concentration and a thin gate oxide film. Where electronic circuits widely differing from each other in the required function are formed on the same semiconductor substrate as in the one-chip system noted above, the conventional manufacturing process gives rise to a serious problem that the manufacturing steps are increased for achieving the various functions, leading to a high manufacturing cost.
As described above, even if it is intended to reduce the manufacturing cost of a semiconductor device by using a semiconductor substrate having a large diameter, it is necessary to develop and introduce a fresh new manufacturing apparatus capable of processing the large semiconductor substrate. In addition, where a semiconductor substrate having a large diameter is used for mass production of a semiconductor device, it is necessary to cope with use of a large semiconductor substrate in every single manufacturing step, leading to requirement of a intensive capital investment. Further, where a semiconductor substrate having a diameter larger than that of the semiconductor substrate used in the stage of the research and development is used for mass production of a semiconductor device, the efficiency of the research and development is impaired. These economical losses offset the merit of the improved productivity achieved by the use of a semiconductor substrate having a large diameter.
In addition, it is technically difficult to prepare a semiconductor substrate itself free from crystal defects over a large area of the substrate, leading to a high unit cost of the semiconductor substrate having a large diameter.
Further, where flaw or miscarriage such as incompletion of a certain process has taken place in a part of the semiconductor substrate, the defective part makes it unavoidable to discard the other satisfactory part of the semiconductor device or to continue to apply the subsequent manufacturing steps to even the inoperable devices leading to a low yield.
Still further, where common manufacturing steps are employed for achieving a one-chip system, the number of manufacturing steps is increased and the manufacturing step is made complex, leading to a high manufacturing cost.